Malondialdehyde (MDA) is produced in mammalian tissues by enzymic and non-enzymic fragmentation of prostaglandin endoperoxides and by peroxidation of polyunsaturated lipids. MDA has been reported to be mutagenic and carcinogenic which raises the possibility that it is a mediator of spontaneous carcinogenesis. Althugh early reports probably overestimated the mutagenicity and carcinogenicity of MDA, we have found that higly purified MDA is weakly mutagenic. It is possible that this is due to the presence of a small amount of a potent mutagenic impurity in the MDA preparations. In order to unequivocally establish whether MDA is mutagenic, we propose to prepare it by complementary procedures, analyze its purity, and determine its mutagenicity in Salmonella typhimurium strains. Preliminary data from ourlaboratory indicates the MDA is rapidly combusted to CO2 following intraperitoneal injection into mice. The pathway of metabolism has not been established but can be suggested based on the comparison of the extent of combustion of related compounds. Quantitative comparisons of the extent of combusions of specifically 14C-labeled MDA, Beta-alanine, acetic acid, and malonic acid will be conducted to indicate a likely pathway for the metabolism of MDA in vivo. The ability of slices from various mouse organis to combust 14C-MDA to 14CO2 will be measured to determine the tissue distribution of MDA combustion activity. Tissues with high activity for MDA combusion should be least susceptible to its mutagenic and carcinogenic action. The extent of covalent binding of 3H-MDA to DNA will be measured in vitro. The 3H-MDA will be prepared by a procedure which we have developed in our laboratory. Identification of the bases likely to be involved in the binding will be performed by a combination of deoxy nucleoside competition and depurination experiments. Standards of deoxynucleoside-MDA adducts will be prepared and identified by spectroscopic methods. Once their structures have been determined, they will be compared to the adducts isolated following the reaction of 3H-MDA with DNA. These studies will provide a quantitative and qualitative biochemical basis for the evaluation of the involvement of MDA in cellular pathology.